Sergei D. Kirik

A crystal structure of ultra-dispersed form of polytetrafluoroethylene based on X-ray powder diffraction data

An X-Ray powder diffraction study of ultra-dispersed polytetrafluoroethylene was carried out. As well as a regular polytetrafluoroethylene the ultra-dispersed form contents a high proportion of the crystalline phase. The X-ray diffraction pattern could be described with two-dimensional hexagonal unit cell [a=5.685(1) A, symmetry group p6mm]. Structural modeling with a continuous electron density approach as well as with a discrete disordered atoms distribution was accomplished. The model was refined using the Rietveld method. The structure is characterized by a spiral arrangement of polymers (CF 2 -) n along the z -axis with complete mutual disordering by rotational displacement around z , as well as a partial molecular translation along the z -axis. Molecular disordering results in a systematic absence of reflections with 1≠0 and as a sequence in two-dimensional unit cell effect. The presence of complete rotational disordering distinguishes the ultra-dispersed form of polytetrafluoroethylene from the standard one (fluoroplast-4), where only partial disordering is observed.

[Pd(CH3COO)2]n from X-ray powder diffraction data.

The water-insoluble title compound, catena-poly[palladium(II)-di-mu-acetato-kappa4O:O], [Pd(C2H3O2)2]n, was obtained from a nitratopalladium solution and acetic acid as a pale-pink powder. Ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. Patterson and Fourier syntheses were used for atom location and the Rietveld technique was applied for the final structure refinement. The structure consists of palladium acetate complexes connected into polymeric chains running along b, in which two Pd atoms are bridged by two acetate groups that are in a cis configuration with respect to one another. The unique Pd atom lies on a site with 2/m symmetry and the acetate moieties have imposed m symmetry; these are joined into infinite chains running along the b direction. The shortest Pd...Pd distance in the row is 2.9192 (1) A. The planes of adjacent palladium complexes are inclined towards each other, the angle between the planes being approximately 30 degrees.

X-ray diffraction analysis of mesostructured materials by continuous density function technique

Abstract A continuous density function technique has been developed for X-ray diffraction (XRD) structural investigations of mesostructured materials. The technique is designed for the analysis of the density distribution in materials exhibiting nanoscale (2-50 nm) ordering of structural elements without atomic long-range order. The results of structure investigations of a series of silicate, metallosilicate and carbon mesostructured materials with hexagonal and cubic symmetry are presented.

CdBiO2Cl: synthesis and powder structure solution

The title compound, cadmium bismuth dioxide chloride, CdBiO2Cl, was obtained as a white powder by reaction of solid BiOCl with CdO at 973 K. Ab initio crystal structure determination was carried out using X-ray powder diffraction techniques, including direct methods for atom location and Rietveld fitting for the final refinement. Being monoclinic, the crystal structure can be related to tetragonal Sillen layered phases. The main structural elements present are CdBiO2+ pleated metal-oxygen layers alternating with Cl layers along the c axis, whereas along the b axis, all atoms are on mirror planes. The formation of a strong Cd-Cl bond draws the layers together, causing layer deformation and a monoclinic distortion in the layer arrangement.

NaF-KF-AlF3 System: Phase Transition in K2NaAl3F12 Ternary Fluoride

Phase formation in the NaF-KF-AlF3 system, in the vicinity of the K2NaAl3F12 composition, has been studied. The samples have been prepared by melting the starting components at 650 °C. A new phase has been revealed, which appeared to be a low-temperature form of the well-known K2NaAl3F12 ternary fluoride obtained by the hydrothermal synthesis method. The high-temperature form melts at 598 °C and is stable in a narrow temperature region of about 15 deg below the melting point. Thermal analysis, high temperature X-ray diffraction, IR-spectroscopy, X-ray fluorescence, and X-ray powder diffraction crystal structure analysis have been applied to study the composition, crystal structure, and thermal properties of the low-temperature phase. The crystal structure consists of trigonal-hexagonal two-dimensional (2D) grids built from the [AlF6] octahedra connected via vertices. The 2D grids have a specific wave-like conformation with a wavelength of 11.88 Å and an amplitude of 0.46 Å. There is a shift of the adjacent grids relative to each other. Because of this shift, the space between the grids changes. The shift leads to the formation of pores adapted to potassium and sodium ions. The reasons for the wave-like structure of layers are discussed. It is shown that the two polymorphic forms differ in the order of cation occupations.

[Pd8(CH3COO)8(NO)8]: solution from X-ray powder diffraction data.

The water-insoluble title compound, octakis(mu-acetato-kappa2O:O)octakis(mu-nitroso-kappa2N:O)octapalladium(II), [Pd8(CH3COO)8(NO)8], was precipitated as a yellow powder from a solution of palladium nitrate in nitric acid by adding acetic acid. Ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. Patterson and Fourier syntheses were used for atom locations, and the Rietveld technique was used for the final structure refinement. The crystal structure is of a molecular type. The skeleton of the [Pd8(CH3COO)8(NO)8] molecule is constructed as a tetragonal prism with Pd atoms at the vertices. The eight NO- groups are in bridging positions along the horizontal edges of the prism. The N and O atoms of each nitroso group coordinate two different Pd atoms. The vertical edges present PdPd contacts with a short distance of 2.865 (1) A. These Pd atoms are bridged by a pair of acetate groups in a cis orientation with respect to each other. The complex has crystallographically imposed 4/m symmetry; all C atoms of the acetate groups are on mirror planes. The unique Pd atom lies in a general position and has square-planar coordination, consisting of three O and one N atom.

Powder-diffraction solutions of the crystal structure of [Pd(NH 4 ) 3 ]C 2 O 4

The crystal structure of [Pd(NH 3 ) 4 ]C 2 O 4 was determined from X-ray powder data. The crystals are triclinic with unit-cell parameters: a =7.0807(7) A, b =7.0806(7) A, c =3.8011(5) A, α=91.910(1)°, β=98.665(1)°, γ=97.283(1)°, S . G .= P −1, Z =1, V =187.11 A 3 . All non-hydrogen atoms were located from the Patterson map. The structure was refined by the Rietveld technique: R p − b =6.88, R wp =6.51, R B =2.66. The crystal structure of [Pd(NH 3 ) 4 ]C 2 O 4 is built from two types of elements: [Pd(NH 3 ) 4 ] 2+ and C 2 O 2− 4 . Cations [Pd(NH 3 ) 4 ] 2+ form columns along c with distances (Pd–Pd)=3.8011 A. C 2 O 2− 4 anions occupy places in the middle of the unit cell between layers of [Pd(NH 3 ) 4 ] 2+ . The compound is stable up to 200 °C and then decomposes, giving Pd powder.

LiNa2AlF6: a powder structure solution.

Lithium sodium aluminium fluoride was obtained as a white powder by melting a stoichiometric mixture of AlF(3), NaF and LiF at 1223 K, and then cooling to 923 K and sintering at this temperature for 4 h. The ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. The monoclinic structure of LiNa(2)AlF(6) can be related to cubic elpasolite. The Li and Al atoms lie on inversion centres. The main octahedral AlF(6) structural elements are not deformed, but are rotated slightly with respect to the unit-cell axes. The Li atoms have octahedral coordinations, whereas the Na atoms have cubo-octahedral coordinations. The Na coordination polyhedron is distorted in comparison with that of elpasolite.

cis -Amminedichloroisopropylamineplatinum(II) by X-ray powder diffraction analysis

The title compound, [PtCl2(C3H9N)(NH3)], was obtained from potassium tetrachloroplatinate(II) by a two-step route. Ab initio crystal structure determination was carried out using X-ray powder diffraction techniques. Patterson and Fourier syntheses were used for the atom locations and the Rietveld technique for the final structure refinement. The Pt coordination is close to planar, with Cl atoms in a cis orientation. Molecules are combined into groups of two molecules, with antiparallel PtN2Cl2 planes and a shortest Pt...Pt distance of 3.42 angstroms. The molecule groups are packed in a parquet motif into corrugated layers parallel to ab. The molecules in the layers are linked by H-N...Cl hydrogen bonds.

08-P-14-Comparative study of the wall properties in highly-ordered silicate and aluminosilicate mesostructured materials of the MCM-41 and SBA-15 types

Publisher Summary This chapter discusses a comparative study of the wall properties in highly ordered silicate and aluminosilicate mesostructured materials of the MCM-41 and SBA-15 types. X-ray diffraction (XRD) structural modeling based on a continuous electron density representation and textural analyses by the combined XRD-adsorption method is applied to quantify distinctions in the wall structure of the MCM-41 and SBA-15 types of mesostructured materials.